What is the difference between a simple backend and an easy backend ? Not sure that I pickup the nuance
A easy system might be very complexly built, but presents and easy interface for you to use. If complex it would be hard to understand how it is built and how to modify.
Basically simple describes how the system is built, while easy describes how much you need to know to use it.
They are orthogonal, so a system can be both complex and easy, both simple and hard.
If the use of "pickup" instead of "pick up" was intentional, that's hilarious.